Reminder & Announcement

Transcription

1 Reminder & Announcement Starting the week of October 15 th Group 1 is doing the tutorial on Strong Acids and Bases and Redox. Group 2 is doing the Acid/Base lab. I am away next Monday thru Wednesday. Professor Martin will substitute for me in class and tutorial.

2 The Periodic Table When the elements are grouped together on the basis of their physical and chemical properties, they fall into groups illustrated by the periodic table First devised by D. Mendeleev long before the advent of quantum theory

3 Who was Mendeleev? Demitri Mendeleev was a Russian scientist. He was born 1834 and died Although not the only chemist of his day to make tables of elements, he was the first to use his table to predict the existence of other elements such as Ge, Ga and Sc. As Director of the Russian Bureau of Weights and Measures, he decided that Russian vodka should be 80 proof (40% ethanol).

4 Groups Periods (Horizontal Rows)

5 20 th century chemistry has shown that these groups have similar electronic configurations This demonstrating that the behavior of the elements is a consequence of the number and configuration of their electrons only: The atomic nucleus is unimportant chemically The electrons that are the most important in determining the properties of an element are those in the highest energy, incompletely filled orbitals: the valence electrons Main group elements are those with s or p subshells being filled, with other subshells being full or empty Those with d orbitals being filled are termed transition metal elements. Each d subshell holds 10 electrons Elements in the f-block are those with f-orbitals being filled. These orbitals hold 14 electrons. The elements with the 4f orbitals being filled are called the lanthanides Those with the 5f orbitals being filled are called the actinides

6 Since elements in any one group have the same number of valence electrons, it is no surprise that they have similar chemical properties Group 1A Alkali metals valence config. = ns 1 Li, Na, K, Rb, Cs, Fr Group 2A Alkaline Earths valence config. = ns 2 Be, Mg, Ca, Sr, Ba, Ra Group 3A (13) B, Al, Ga, In, Tl Old English for base Earth = old English for nonmetallic substance insoluble in water valence config. = ns 2 np 1 Group 4A (14) C, Si, Ge, Sn, Pb Group 5A (15) N, P, As, Sb, Bi valence config. = ns 2 np 2 valence config. = ns 2 np 3 Group 6A (16) Chalcogens valence config. = ns 2 np 4 O, S, Se, Te, Po (Greek for ore former ) Group 7A (17) Halogens valence config. = ns 2 np 5 F, Cl, Br, I, At (French and Greek Halos = salt; genes = production) Group 8A (18) Noble gases valence config. = ns 2 np 6 He(1s 2 ), Ne, Ar, Kr, Xe, Rn

7 Noble gases are extremely stable and not very reactive due to their full valence shell. (They can undergo some chemical reactions). Other elements can lose or gain electron to attain the same electronic configuration as these noble gases. For example: For example: K tends to give away one electron and Cl to accept one electron to attain the Ar configuration

8 1. Atomic Size Periodic Trends in Atomic Properties The atomic radius reflects the distance from the nucleus to the highest occupied electronic orbital. Therefore we expect the following: i) Atomic radii increase from top to bottom within a group. For example: r(li) < r(na) < r(k) < r(rb) < r(cs) However ii) Atomic radii decrease from left to right across a period For example: r(li) > r(be) > r(b) > r(c) > r(n) >r(o) > r(f) This is because the electrons in the same n-orbital (here n = 2) are more strongly attracted to the greater number of protons in the nuclei of the heavier elements iii) Cations are smaller than the neutral parent atom. For example r(li + ) < r(li) iv) Anions are larger than the neutral parent atom. For example r(cl - ) > r(cl)

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10 Relative atomic radii in picometers

11 Atomic Sizes and Radii (An aside: not responsible for this) There is no one way to define the size of an atom, like we can define the size of a billiard ball. This is a limitation of quantum theory. Common approaches: Single-bond covalent radii - radii assigned within a covalent bonding situation. Ionic radii - radii assigned to ions of the elements in predominantly ionic compounds Metallic or van der Waals radii - distances. non-bonded contact

12 Could also be taken as van der Waals radius

13 2.Ionization Energies Ionization energy, IE, is the energy required to remove one electron from an atom or ion; an endothermic process that is, A A e - H = +ve The energy, in kj mol -1, required to remove 1 electron from the neutral atom (1 st ionization limit) depends on the orbital in which the electron resides Two general trends: 1.) IEs decrease down a group (an electron removed from an orbital more distant from the nucleus is less tightly bound) 2.) IEs increase from left to right increase from left to right across a period (electrons being removed from orbitals of equal n are subject to increasing nuclear attraction)

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